Updated Aug 2026
Oregon Lake Water Quality
Water quality grades for 99 monitored lakes across 25 counties.
Across Oregon, 99 lakes carry an active water-quality grade spread over 25 counties. The underlying measurements come from the Oregon Department of Environmental Quality, alongside federal programs and volunteer monitoring networks. A-grade lakes are scarce in Oregon: about 13% of the dataset. Most lakes here sit in C or D — productive, often shallow, frequently algal in late summer.
Most Oregon lakes sit in the mesotrophic band — moderate productivity, decent clarity, capable of supporting both warm-water and cool-water fisheries. This is the band where well-managed working lakes tend to land. Wallowa ranks highest on average county grade (A). Coos sits lowest. With only 25 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Grade Distribution
All 99 Oregon lakes in the index: 73 (73.7%) carry an A–F grade and 26 (26.3%) are not rated, because they lack enough recent nutrient or algae sampling to support a letter.
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Top-Graded Oregon Lakes
The highest water-quality grades in Oregon — clarity, depth, and A-F grade at a glance.
Lake Map
Explore Oregon Lakes
Oregon reports, fishing & travel
Reservoirs in Oregon
View all 50 reservoirs →50 of 99 Oregon lakes (51%) are man-made reservoirs in the USACE National Inventory of Dams. 46 carry a High or Significant hazard rating. The oldest matched dam dates to 1908.
EPA-Impaired Lakes in Oregon
View all 67 impaired lakes →67 of 99 Oregon lakes (68%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 26 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Oregon Fishing & Recreation
Licenses, regulations, records, and where to fish across Oregon.
Counties
All 25 Oregon counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of graded lakes, or pick a different state.
Top 25 Cleanest Lakes
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity | Trophic | Access |
|---|---|---|---|---|---|---|
| 1 | ACrescent Lake | Klamath | A | 42.2 ft | Oligotrophic | ✓ Public |
| 2 | ACrescent Lake | Klamath | A | 51.7 ft | Oligotrophic | Not recorded |
| 3 | AOdell Lake | Klamath | A | No recent samples | Oligotrophic | ✓ Public |
| 4 | ACrescent Lake | Klamath | A | No recent samples | Oligotrophic | ✓ Public |
| 5 | ACougar Lake | Lane | A | No recent samples | Oligotrophic | ✓ Public |
| 6 | AApplegate Lake | Jackson | A | No recent samples | Oligotrophic | ✓ Public |
| 7 | ALake of the Woods | Klamath | A | No recent samples | Oligotrophic | ✓ Public |
| 8 | AGalesville Reservoir | Douglas | A | No recent samples | Oligotrophic | ✓ Public |
| 9 | AFourmile Lake | Klamath | A | No recent samples | Oligotrophic | ✓ Public |
| 10 | AWallowa Lake | Wallowa | A | No recent samples | Oligotrophic | ✓ Public |
| 11 | AHenry Hagg Lake | Washington | A | No recent samples | Oligotrophic | ✓ Public |
| 12 | AGreen Peter Lake | Linn | A | No recent samples | Oligotrophic | ✓ Public |
| 13 | ATimothy Lake | Clackamas | A | No recent samples | Oligotrophic | ✓ Public |
| 14 | BDetroit Lake | Marion | B | No recent samples | Mesotrophic | ✓ Public |
| 15 | BBlue River Lake | Lane | B | No recent samples | Oligotrophic | ✓ Public |
| 16 | COdell Lake | Klamath | C | 22.3 ft | Oligotrophic | Not recorded |
| 17 | CBilly Chinook Reservoir | Jefferson | C | 4.4 ft | Mesotrophic | Not recorded |
| 18 | COdell Lake | Klamath | C | 18.7 ft | Oligotrophic | ✓ Public |
| 19 | CBilly Chinook Reservoir | Jefferson | C | 8.4 ft | Mesotrophic | Not recorded |
| 20 | CWickiup Reservoir | Deschutes | C | 11.2 ft | Mesotrophic | ✓ Public |
| 21 | CLost Creek Lake | Jackson | C | No recent samples | Mesotrophic | ✓ Public |
| 22 | CWillow Lake | Jackson | C | No recent samples | Mesotrophic | ✓ Public |
| 23 | CEmigrant Lake | Jackson | C | No recent samples | Mesotrophic | ✓ Public |
| 24 | CFoster Lake | Linn | C | No recent samples | Mesotrophic | ✓ Public |
| 25 | CEast Lake Hot Springs Boat Ramp | Deschutes | C | No recent samples | Mesotrophic | Not recorded |
25 Lakes Needing Attention
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | FUpper Klamath Lake | Klamath | F | No recent samples |
| 2 | FThief Valley Reservoir | Union | F | No recent samples |
| 3 | FDiamond Lake | Douglas | F | No recent samples |
| 4 | FCold Springs Reservoir | Umatilla | F | No recent samples |
| 5 | FBrownlee Reservoir | Baker | F | No recent samples |
| 6 | FTenmile Lake | Coos | F | No recent samples |
| 7 | FCullaby Lake | Clatsop | F | No recent samples |
| 8 | FLake Billy Chinook | Jefferson | F | No recent samples |
| 9 | FDeschutes River Arm Lake | Jefferson | F | No recent samples |
| 10 | FLake Billy Chinook | Jefferson | F | No recent samples |
| 11 | FMid-North Lake | Klamath | F | No recent samples |
| 12 | FRattlesnake Point Lake | Klamath | F | No recent samples |
| 13 | FUpper Klamath Lake | Klamath | F | No recent samples |
| 14 | FShoalwater Bay Lake | Klamath | F | No recent samples |
| 15 | FAgency Lake South | Klamath | F | No recent samples |
| 16 | FMid-Trench Lake | Klamath | F | No recent samples |
| 17 | FMalheur Lake | Harney | F | No recent samples |
| 18 | FWilliamson River Outlet Lake | Klamath | F | No recent samples |
| 19 | DHaystack Reservoir Campground Boat Ramp | Jefferson | D | No recent samples |
| 20 | DOchoco Lake County Park Boat Ramp | Crook | D | No recent samples |
| 21 | DLake Owyhee | Malheur | D | No recent samples |
| 22 | DLemolo Lake | Douglas | D | No recent samples |
| 23 | DPhillps Lake | Baker | D | No recent samples |
| 24 | DPine Hollow Reservoir | Wasco | D | No recent samples |
| 25 | DUnity Reservoir | Baker | D | No recent samples |
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Source: EPA National Aquatic Resource Surveys and the EPA Water Quality Portal.
More on lake water quality
The top-graded lake in every state we cover, picked grade-first with water clarity as the tie-breaker — plus the states whose winner is still not clean.
State-by-state Secchi champions: the clearest measured lake in each U.S. state we grade, which is not the same as the cleanest nutrient grade.
A data snapshot of the lakes we grade: how the A–F distribution breaks down, the clearest and the greenest states, and where the water is improving.
How lakes are graded A–F on nutrients and algae using EPA ecoregion condition classes, what each letter means in the water, and why an A is not a clearance.